There are a lot of beautiful girls in One Piece,but i will do a top 5 about the most "sensual" girls instead of the most beautiful girls. The most sensual ones to me are:
1- Kalifa. She seemed to get out from a porn movie. Her sensual voice,her sensual attitude in general,her tights...she was very very sensual
2- Reiju. The way she acts after she sucks Luffy's poison....great sensuality!
3- Boa Hancock. Bitchy attitude is sexy
4- Black Mariah. She seems very sensual too
5- Nami. She knows how to be flirty and seduce a man when she needs to steal from him. Sadly we rarely see this side of her in the post-timeskip